Network congestion can affect communication quality, especially for real time communications, such as voice over internet protocol (VoIP), online gaming, video conference, and the like. In a video conference example, video image data packets can be piled up in a buffer of a router during times of heavy network congestion, and therefore, video image transmission delay can be long. Worse yet, the video image data packets can be dropped by the router when the buffer is low on storage space, which can result in a video conference image that is choppy. On the other hand, real time communications can attempt to occupy a large amount of network communication resources, which can increase network congestion. For example, a video conference may transmit high resolution video image in an already congested network, and thus exacerbate an already bad network congestion situation.
In a technique to relieve network congestion, transport protocols, such as TCP, can slow down packet sending rate, and thus reduce an amount of packets that enter the network. In another technique, a router can selectively drop low priority packets, while permitting high priority packets go through.